My friend Pan Suefen refers to this kind of preparation as a "dry" stir-fry, because there's no sauce. The focus here is on earthy mushrooms and brightly flavored bok choy, exploited to their fullest to produce a final result that is greater than the sum of its parts. I love how the dried mushrooms, reconstituted in water, take on a satisfying, slightly chewy texture and a deep umami flavor in the hot oil. The bok choy undergoes a pleasing transformation as well: the crunchy white stem develops a caramelized flavor as it's left alone for a minute with its cut surface in direct contact with the wok, and the leaves wilt slightly, acquiring a mild sweetness as they cook.